1. Field of the Invention
The present invention relates to a protecting agent-supplying device which supplies an image bearing member-protecting agent to an image bearing member provided in image forming apparatuses such as copiers, facsimiles and printers, a process cartridge including the protecting agent-supplying device, an image forming apparatus including the protecting agent-supplying device.
2. Description of the Related Art
In image forming apparatuses (e.g., copiers, facsimiles and printers) having an image bearing member (e.g., a photoconductor made of, for example, a photoconductive material, or the like), the image bearing member is rotated and subjected sequentially to a charging step, an exposing step, a developing step, a transfer step and a fixing step, etc. for image formation.
In the charging step, a surface of the image bearing member is charged with a charging member such as a charging roller. In the exposing step, a latent electrostatic image is formed on the surface of the image bearing member whose surface has been charged in the charging step. In the developing step, charged toner particles are made to adhere to the latent electrostatic image on the image bearing member surface, to thereby form a visible image. In the transfer step, the visible image is transferred from the image bearing member onto a recording medium (transfer medium) such as paper. In the fixing step, the visible image transferred onto the recording medium is fixed thereon with, for example, heat, pressure or gaseous solvent. Through these steps, an output image is formed on the recording medium.
The developing method in the developing step is roughly classified, depending on the method of charging toner particles, into a two-component developing method and a one-component developing method. In the two-component developing method, toner particles are stirred/mixed with carrier particles and are frictionally charged. In the one-component developing method, toner particles are charged with no use of carrier particles. The one-component developing method is further classified into a magnetic one-component developing method and a non-magnetic one-component developing method, depending on whether or not the developer bearing member (for bearing toner particles) retains toner particles by a magnetic force.
Of these developing methods, the two-component developing method is often employed in, for example, copiers required for high-speed processing and developing reproducibility, and complex machines employing such copiers, in terms of charging stability of the toner particles, charge rising property, long-term stability of image quality, and other requirements. Meanwhile, the one-component developing method is often employed in the compact printers and facsimiles.
In recent years, color images are generally formed, and thus, demand has increasingly arisen for high image quality and stability of image quality. These requirements are intended to be met not by improving the developing method, but by decreasing the average particle diameter of toner particles and using more spherical toner particles. For example, toners produced with the polymerization method are seen on the market. These toners have advantageous features in that they have less angular portions and a uniform average particle diameter, as compared with toners produced with the pulverizing method. In addition, the polymerized toners contribute to not only improvement of image quality but also saving of production energy.
In the charging step, recently, a charging device having the following structure is used in many cases, because it is advantageous in terms of achieving low ozonization and low electric power: the charging device includes, as a charging member, a charging roller obtained by forming a conductive member into a roller shape, and the charging roller is disposed closely to or in contact with a surface of an image bearing member, and then a voltage is applied to a space between the charging roller and the image bearing member so as to charge the surface of the image bearing member.
In such a charging device, a method of applying charge bias obtained by superimposing a direct-current voltage on an alternating-current voltage is used to uniformly charge a surface of an image bearing member. The image forming apparatus using this method needs a large amount of the alternating-current to obtain a desired charged electric potential, compared to the charging method using direct-current alone, and it is necessary to adjust alternating-current frequency to “n” times or more of a linear velocity of an image bearing member (“n” is an integer of 1 or more). For example, when n is 7, and the linear velocity of an image bearing member is 100 mm/sec, 700 (7×100) Hz or higher of the alternating-current frequency is required. When the alternating-current frequency is adjusted to less than “n” times, jitter of period of the alternating-current frequency occurs in an image having uniform intermediate potential such as a half-tone image. Therefore, when a plurality of the linear velocities of the image bearing members are provided in one image forming apparatus, the alternating-current frequency is adjusted according to each of the linear velocities, to thereby obtain charging ability similar to that obtained by the charging method using direct-current alone.
The image bearing member having undergone the transfer step has, on the surface thereof, residual toner components which have not been transferred onto the recording medium. When charged again in the charging step in this state, the image bearing member is not uniformly charged in many cases. Thus, in general, a cleaning step is additionally provided after the transfer step and before the next charging step. In the cleaning step, the toner components and other foreign matters (e.g., paper dust) remaining on the image bearing member are removed with a cleaning member such as a cleaning blade, and the image bearing member surface is sufficiently cleaned before the charging step.
In recent years, cleaning performance for toner has been remarkably improved in the cleaning steps, and the recently-used small and highly spherical toner particles can be cleaned. Such improved cleaning performance reduces stain of the charging member, and the service life of the charging member is elongated. Moreover, such improved cleaning performance prevents toner particles from running through a cleaning blade, and the cleaning blade is less abraded, to thereby elongate the service life thereof.
The image bearing member receives various physical or electrical stresses in the above steps, and the state thereof changes over time, especially after long-term use. For example, as has been known, the stress caused by the friction in the cleaning step abrades and scratches the image bearing member, and also abrades the cleaning member in the cleaning step. Thus, conventionally, there have been proposed methods of supplying a lubricant or lubricating components and of forming a film on the image bearing member surface using the lubricant or lubricating components, in order to reduce the friction force between the image bearing member and the cleaning member.
For example, some patent literatures disclose techniques of forming a lubricant film on the surface of a photoconductor (image bearing member) by supplying a lubricant as the image bearing member-protecting agent onto the photoconductor surface to elongate the service lives of the photoconductor and the cleaning member (see, for example, Japanese Patent Application Publication (JP-B) No. 51-22380, and Japanese Patent Application Laid-Open (JP-A) Nos. 2007-293240, 2002-268397, and 2006-350240). Using the above techniques, the stress applied to the image bearing member in, for example, the charging step can be easily reduced.
Meanwhile, as the component of the lubricant, a lubricant mainly containing a fatty acid zinc salt (see, for example, JP-B No. 51-22380 and JP-A Nos. 2007-293240, and 2002-268397) and a lubricant formed by incorporating an inorganic lubricant into a fatty acid zinc salt (see, for example, JP-A No. 2006-350240) have been known. The latter lubricant decreases in lubricity to a less extent than in the former lubricant, even when receiving the stress due to discharge in the charging step.
That is, it has been known that the former lubricant promptly loses its lubricity due to discharge performed near an image bearing member in the charging step. As a result, the lubricities of the cleaning blade and the image bearing member are impaired, and the toner particles run through between the cleaning blade and the image bearing member, causing image failure. The toner running through significantly occurs in the case of the recently-used small and highly spherical toner particles. Moreover, since with use of the former lubricant the toner running through frequently occurs, and the cleaning blade is abraded, and the service life of an image forming apparatus may be shortened. By contrast, the latter lubricant does not easily decrease in the lubricity, even when a surface of an image bearing member receives an electrical stress in the charging step. Moreover, the latter lubricant forms coating film over an entire surface of an image bearing member and high lubricity is maintained.
In one known configuration in which a lubricant is supplied to the photoconductor surface, the lubricant is formed into a solid bar shape, and a brush which is a rotation member is rubbed against a solid bar lubricant so that the lubricant is scraped off and supplied to the photoconductor surface (see, for example, JP-A Nos. 2007-293240, 2002-268397 and 2006-350240).
In another known configuration in which a lubricant is supplied to a photoconductor, a solid lubricant is elastically brought into contact with a brush to maintain constant, for a long period of time, the amount of the lubricant supplied to the photoconductor (see, for example, JP-A Nos. 2007-293240 and 2002-268397). Meanwhile, compression molding and melt molding are known as methods of solidifying a lubricant into a bar shape (see, for example, JP-A No. 2006-350240).
It has been known that elements of determining an amount of supplying a lubricant to an image bearing member include presence or absence of a toner adhering to a brush, as well as a change of a brush over time. This is because when the toner adheres to the brush the toner scrapes off a lubricant with the brush. By using the latter lubricant described above, the toner running through does not occur, and the toner does not adhere to the brush. Thus, the amount of supplying the lubricant to the image bearing member only depends on the deterioration of the brush. Then, when the brush deteriorates over time, the consumption of the lubricant decreases, and the image bearing member is not sufficiently protected, causing filming. Thus, in order to sufficiently supply the lubricant to the image bearing member for a long period of time, it is necessary to press the lubricant against the brush at high pressure from the beginning of supplying the lubricant. The pressure applied to the latter lubricant is set to be at least approximately 1.2 times higher than that applied to the former lubricant.
However, in the case where the pressure is increased, when the rotational force of the brush is applied to the solid lubricant during the rotation of the brush, the lubricant is elastically brought into contact with the brush. The solid lubricant inclines toward the rotational direction of the brush, and the brush may be brought into contact with a side surface of the lubricant. In such case, the pressure of the brush is not uniformly applied to the solid lubricant in the longitudinal direction of the solid lubricant, and the lubricant is not uniformly scraped off in the longitudinal direction thereof. As a result, the frictional sliding surface of the lubricant is nonuniformly consumed. Once the lubricant is nonuniformly consumed, it is not corrected, but rather progresses. Thus, a nonuniformly consumed part is consumed faster than the set service life, causing shortening of the service life of an entire image forming apparatus.
In this point, there is a proposal of a technique that with the use of the former lubricant formed into a solid, the lubricant is disposed upstream in the rotation direction of the brush, so as to suppress deterioration of the brush over time, i.e., tilt of brush fur, due to disuse of the fur for a long period of time (JP-A No. 2002-268397).
However, since the above-described technique uses the former lubricant, the former lubricant promptly loses its lubricity due to discharge performed near an image bearing member in the charging step. As a result, the lubricities of the cleaning blade and the image bearing member are impaired, and the toner particles run through a gap between the cleaning blade and the image bearing member, causing image failure. The toner running through significantly occurs in the case of the recently-used small and highly spherical toner particles. Moreover, since with use of the former lubricant the toner running through frequently occurs, a cleaning blade is abraded, and the lubricant is nonuniformly consumed, causing shortening of the service life of an image forming apparatus. Moreover, the technique is not positioned as a countermeasure to the nonuniform consumption of the lubricant. In the technique, there is no specific disclosure of a shift value.